Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$83.80	5.109%	$88.0813	$88.08	$88.10	$88.10
Purchase #2	$60.57	7.153%	$64.9026	$64.90	$64.90	$64.90
Purchase #3	$228.77	10.838%	$253.5641	$253.56	$253.55	$253.60
Purchase #4	$158.74	4.554%	$165.969	$165.97	$165.95	$166.00
Purchase #5	$158.67	5.469%	$167.3477	$167.35	$167.35	$167.30
Purchase #6	$96.46	7.706%	$103.8932	$103.89	$103.90	$103.90
Purchase #7	$30.37	10.777%	$33.643	$33.64	$33.65	$33.60
7 purchase totals =	$817.38		$877.4009	$877.39	$877.40	$877.40